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Topic: Erratic values piezofilm sensor (Read 610 times) previous topic - next topic

klausb

Hi,
  I'm new in arduino. I'm trying to work with a piezo film sensor, arduino duemilanove and max/msp.
I connected the sensor with a zener diode 5v and R 1M.
It's working but I reveive a permanent erratic signal from the arduino analog input, I can see some changes produced by the sensor but only when these are big changes and in the middle of a cloud of values randomizing all the time.
I appreciate any idea or comment.
Thank you

k

Tim Stamp

Try adding a small capacitor (metal film or polyester) between ground and the output of the sensor. This might smooth the output enough for you to get a steady reading.

If the capacitor is too large however it might 'slur' the responses and might reduce the accuracy, and spikes in the output feed probably won't be recognised at all.

klausb

Thank you Tim!
I will try it tomorrow and I let you know the results.

Grumpy_Mike

Quote
I reveive a permanent erratic signal from the arduino analog input


That is because it is picking up noise due to the fact that you have a very high input impedance. However, if you lower it by say putting a 100K across the input to ground you will also reduce the size of the signal you get. It's a compromise between the sensitivity and the noise pickup. Try different values to ground to find what suites your setup.

klausb

Thank you Tim Stamp and Grumpy_Mike.
I tried today with a 0.1 uf capacitor and everything is working fine.
I will continue trying with different capacitors and resistors values to obtain the best results.
Thank you for a good lesson!!!

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